The present invention relates in general to the machining of parts or workpieces by a plurality of machining stations using transfer units or fixtures transported by a gantry system, and, more specifically, to such a transfer unit or fixturing system providing quick, automated connects and disconnects with a machining station.
In the manufacturing of certain cast metal products, it is not possible to achieve the final part shape and tolerances by casting alone. Part manufacture usually includes several machining operations that must be applied to the original casting, such as drilling, boring, milling, cutting, and tapping. Products of this type include engine manifolds, wheels, brake rotors, and suspension components such as steering knuckles, control arms, and cross members.
In mass production, it is necessary to organize a manufacturing process with high reliability, short cycle times, easy maintenance, and worker safety while minimizing cost and space requirements. It is also highly desirable to achieve flexibility of the manufacturing process and the manufacturing equipment so that the process and equipment can be adapted at low cost to changes in part design, part mix, or part quantities.
Manufacturing systems utilizing automation are preferred because of increased consistency and reduced time and cost. Automated machining stations typically receive a workpiece (e.g., an unfinished casting) mounted on a fixture (also called a pallet) and automatically perform the desired machining operations on the workpiece. The workpieces may be delivered to and removed from the machining station either manually or automatically by a conveyance.
Various types of machining stations are known. Dedicated stations are constructed to perform a fixed set of operations and cannot be easily adapted to perform other tasks. Dedicated stations usually have a cost advantage when a large volume of parts is to be made and no significant design changes are to occur during a long production run. Another type of station is the computer-numerically-controlled (CNC) machine, which is programmable to perform a variety of machining operations and has advantages of being able to produce parts with a lower number of machining stations and therefore requiring less relocation of a workpiece during manufacture. In addition, CNC machines are more easily adapted to new products or processes and can reduce overall capital investment for a changeover. A typical CNC machine has programmable multidimensional movement of both the tool head and the table that receives the fixture and workpiece.
An especially adaptable type of CNC machine is the flex turret cell which employs a multi-spindle head that automatically reconfigures itself to use selected ones of several tools contained on the multi-spindle head. The multi-spindle head usually comprises a gearbox with multiple output shafts (a different tool on each shaft) driven by a common input shaft. The head is indexed between separate operations while a workpieces remains at the machining station, which improves cycle time and accuracy.
Nevertheless, previous automated systems have suffered from various drawbacks. For example, transfer of workpieces between work stations has remained labor intensive, slow, and/or inflexible (i.e., not easily adaptable to process changes or substitutions). A single workpiece may need to be swapped between various fixtures corresponding to different machining stations when the particular set of machining operations to be performed on the workpiece occurs at several different machining stations. Overall accuracy suffers due to a loss of an exact registration in a reference position between fixtures. Another disadvantage has been the inaccessibility of the CNC machines during operation, making observation and maintenance more difficult.
These disadvantages are overcome by the present invention.
It is an object and advantage of the present invention to provide a transfer unit with quick connect and disconnect for a flexible manufacturing line and manufacturing process providing flexibility and adaptability to variation, improved maintenance of reference position on the fixture during manufacture, improved accessibility to machining stations during operation, and increased safety.
In one aspect, the present invention provides a quick-connect fixturing system for automated manufacturing comprising a transfer unit for holding a workpiece and a machining table for securing the transfer unit at a machining station. The transfer unit includes 1) a plate having a bottom side with a first radial locating feature and a first z-axis locating pad, 2) a shank extending from the bottom side of the plate and having a retention stud, the shank having a shank registration taper, 3) at least one clamp for holding the workpiece, and 4) at least one pick-up extension by which the transfer unit is lifted and carried. The machining table includes 1) a trap for receiving the shank and having a trap registration taper to mate with the shank registration taper, 2) a second radial locating feature to mate with the first radial locating feature, 3) a second z-axis locating pad to mate with the first z-axis locating pad, and 4) a retention mechanism for securing the retention stud so that the transfer unit is located in a predetermined reference position.